Hepatitis C is one of the most common causes of chronic liver disease world-wide. It has been estimated that globally there are 200 million hepatitis C virus (HCV) infected individuals. In the United States, there are approximately 4 million HCV infected individuals accounting for 8,000-10,000 deaths annually. HCV-related cirrhosis is responsible for 30% of adult liver transplantations in this country. The natural history of chronic hepatitis C virus (HCV) infection varies from spontaneous resloution to slowly progressive liver disease to development of cirrhosis within 20 years of infection. Very little is known about the mechanisms of HCV-induced liver injury and the factors that determine the rate of progression of chronic hepatitis C. Several studies have identified a subset of patients with chronic HCV infection who have persistently normal alanine aminotransferase (ALT) levels. While some of these patients have chronic hepatitis on liver biopsy, the majority have no or non-specific changes only. Careful comparison of these patients with those who have abnormal ALT levels may identify factors that differentiate these two groups of patients thus leading to improvement in our understanding of the pathogenesis of HCV-induced liver disease.